1. Field of the Invention
The present invention relates to a test pad circuit, and in particular relates to a display circuit having a test pad on a glass substrate or a system circuit board.
2. Description of the Related Art
Generally, a liquid crystal display device comprises a display penal, a plurality of drivers, and a system circuit board. The display panel is typically a glass substrate. The plurality of drivers comprises a scan driver and a data driver for controlling display units of the display units. There are two kinds of connection between the drivers and the display panel: Chip-On-Film (COF) and Chip-On-Glass (COG). In COG bonding, chips are bonded on a flexible printed circuit board (FPC), in other words, the drivers are directly disposed on a film of the FPC, and the FPC is electrically connected between the display panel and system circuit board. In COG bonding, chips are bonded on the glass substrate, in other words, the drivers are directly disposed on the display panel.
Each driver has a plurality of output pins, and the first and last pins always serve as test pins. In COF bonding, test pads for the test pins are always formed on the bottom surface of the FPC. The FPC must be turned over during test operations of the drivers, thus, test time is increased. In COG bonding, no test pad is formed on the ass substrate. Because the drivers are directly bonded on the glass substrate, a probe station is required to measure output waveforms of the drivers during the test operations of the drivers. Wires on the glass substrate are scraped and damaged by the probe, however, and analysis time is longer.